The present invention relates to the production of images or representations, such as in high-speed printing. More particularly, it relates to a method and apparatus for effectively applying a coloring agent to a recording medium.
Most printing of alphanumeric characters is accomplished by impact printing. That is, in general, a mechanical member of one sort or another which defines all or part of each of the characters to be imprinted, is used to impact an ink or coloring agent medium. However, because of a desire of high-speed printing , less noise, etc., much effort has been expended toward non-impact printing. Some of this effort has been devoted to attempting to provide a commercially successful vapor jet printing mechanism. Such a mechanic is one in which a vaporous coloring agent is transferred via a jetting action to a recording medium.
The approach used most often in vapor jet printing, has been to attempt to print dots which can be arranged to define desired alphanumeric characters. For such a method to provide quality printing with the high resolution necessary, the dots which are provided on the recording medium must be quite small. Moreover, the location of such dots on the recording medium must be accurately controllable.
It will be appreciated that the manner of transferring the coloring agent to the recording medium is an important part of vapor jet printing, particularly in connection with assuring small dot size and accurate control over printing location. Many vapor jet printing arrangements considered in the past have utilized electrical deflection means to provide the transfer. In these schemes the coloring agent is charged and then deflected to a desired location. Such schemes have various disadvantages, a primary one being decomposition of the coloring agent if it is, as in most situations, the vapor state of a sublimable dye. Moreover, most of such arrangements require relatively large spacing between the jet from which the coloring agent emanates and the recording medium, to accommodate the deflection and charging mechanism. The coloring agent, if it is heated such as is typical for a sublimable dye, can be cooled by the atmosphere in such space and solidified before it reaches the recording medium. This, of course, results in a degraded image. Also, most applications for vapor jet printing require multiple jets of one or more coloring agents. The necessity with this approach of controlling the individual jets of coloring agent results in added complexity. Examples of this approach are disclosed in Japanese Patent Publication Nos. 56-2020; 54-71636; and 54-71637.
Other arrangements which have been considered rely simply on the vapor pressure of the coloring agent itself to provide a jetting action, i.e., there is no means for forcibly jetting the vaporous coloring agent. Such a method is described, for example, in Japanese Patent Publication No. 57-1771. One problem with this approach is that in periodic passes of a coloring agent through a jetting nozzle, the coloring agent of one pass may be left in the nozzle because of the low pressure or force used to eject the same. This earlier coloring agent is mixed with the subsequent coloring agent passed through the nozzle and thus changes the amount which is jetted. This deleteriously affects the parameters of printing. Moreover, when the coloring agent is a condensable vapor, it may condense in the nozzle and restrict the same. While heating of vapors has been employed to raise the vapor pressure of the coloring agent, such heating has not solved the nozzle problems.
It also has been proposed to use a gas such as air as a carrier to transport vaporous dyes to the recording medium. Japanese Patent Publication No. 59-22759 is an example of such an arrangement. U.S. Pat. No. 3,950,967 discloses such an arrangement designed for coloring a textile material. Mechanisms which have relied upon this procedure have been less than ideal. One major problem is that it is difficult to control the amount of coloring agent which is transferred during any selected period, i.e., the amount of coloring agent within the gas carrier stream varies. This lack of control, interferes of course, with color proportioning, obtaining desired color densities, etc. Moreover, the use of the gaseous stream of this nature can result in solidification of vaporous coloring agents, such as sublimable dyes in their vapor state. It also should be mentioned that the system of Japanese Patent Publication No. 59-22759 utilizes a relatively expensive laser optical system to form a vaporous coloring agent from solid, sublimable dye rods. It is difficult to incorporate such a system into a multi-head arrangement because of the relatively complex optical and delivery systems utilized in such arrangement, and also to control the gating "on and off" of the formation of the desired vaporous dyes.